Before we get into the details for adjusting layout, I think you should look at the Hum theme because it looks more like your http://www.beccarose.co.uk/ layout to me including the left hand logo area and menu that stays in a fixed position when you scroll:http://humdemo.wordpress.com/

If you think Hum will work out better, switch to it and update the header image from the Appearance → Header page and also look around in the Appearance → Custom Design → Colors page to see what you can do with the colors options there. You'll probably need to adjust some of the colors manually with the CSS editor though. After you're done deciding which theme will work best, post back here or create a new help request to continue getting help with the more specific CSS questions.